1. Field of the Invention
The present invention relates to a vehicle headlamp capable of optimally controlling a light distribution of a lamp depending on a traveling environment of a vehicle, and more particularly to an improved technology capable of forming various types of light distribution patterns by a compact structure.
2. Background Art
It is desirable that a vehicle headlamp accurately realizes various light distribution patterns depending on driving conditions of a vehicle. Since beams emitted from a vehicle headlamp illuminate center parts ahead, there is a case where a sufficient illumination range cannot be secured ahead in a traveling direction when a vehicle is driven around a curve, turned left or right or changed in course etc. For example, there is a swivel-type vehicle headlamp in which a mechanism for laterally turning (rotationally moving) a lighting unit is assembled to a vehicle headlamp, thereby making it possible to secure a sufficient illumination range of beams at the time of traveling around the curve or the like and also obtain a preferable field of view.
The swivel-type vehicle headlamp is constituted in such a manner that the lighting unit is supported on a lamp-body supporting frame member so as to rotationally move in the lateral direction and the lighting unit is allowed to rotationally move and controlled by a control unit depending on traveling conditions of a vehicle. Thereby, beams illuminated from the lighting unit can be changed in the lateral direction, depending on the traveling conditions of the vehicle, a sufficient illumination range of beams can be secured ahead in a turning direction even at the time of traveling around a curve or the like, thus making it possible to obtain a preferable field of view.
However, there is a problem given below when a light-distribution changeable mechanism such as an adaptive front-lighting system (AFS) for optimally controlling (changing) light distribution patterns of a lamp depending on the traveling environment for the purpose of improving the visibility and safety is assembled into an optical projector-type lamp unit (PES).
More specifically, if a single optical projector-type lamp unit having a light quantity capable of forming all light distribution patterns is given a movable structure, there is posed such a problem that the unit is complicated in its structure and accordingly a driving mechanism and a driving source of the optical projector-type lamp unit are made greater in size for driving the unit which is quite heavy and synergistically increased in weight in association with the fact that constituents must be secured for strength.
There is also a problem that since a vehicle headlamp is made into an integrated product which is increased in size as a whole, the lamp is restricted in design, resulting in a difficulty in obtaining good design characteristics. There is another problem that where a light source having an electric discharge/light emission portion is used as a light source, heating from the light source is increased to restrict the selection of materials (low degree of freedom in design).
Further, there has been proposed a vehicle lamp fitting in which insufficient functions of a main lamp unit are imparted and complemented by a sub-lamp unit as a separate body (refer to JP-A-2005-088856). However, the sub-lamp unit is only for complementing color temperature of a light source for the main lamp unit and not for changing a light distribution pattern.